Num Rows computed by EXPLAIN - Hive

[Vivek Sharma]

Hi,


I am new to Hive (just few days of learning).


I am an Oracle Performance Expert and am comparing the Explain feature of Hive 
with Oracle Explain Plan command. I have an Internal Table with around 100 Rows 
in it. However, the Explain command in Hive computes this as 33, which looks to 
be huge discrepancy and cause a performance issues (for a larger table). Wanted 
to know the internal calculations of Hive to come out with the NUM ROWS. The 
output is pasted below (The table actually has 100 Rows) :


hive (vivek)> explain select country, empno from emp;
OK
Explain
STAGE DEPENDENCIES:
  Stage-0 is a root stage

STAGE PLANS:
  Stage: Stage-0
    Fetch Operator
      limit: -1
      Processor Tree:
        TableScan
          alias: emp
          Statistics: Num rows: 33 Data size: 3501 Basic stats: COMPLETE Column 
stats: NONE
          Select Operator
            expressions: country (type: string), empno (type: int)
            outputColumnNames: _col0, _col1
            Statistics: Num rows: 33 Data size: 3501 Basic stats: COMPLETE 
Column stats: NONE
            ListSink

Regards
Vivek